The present invention relates to color photographic materials and processes employing two-equivalent pyrazolone magenta dye-forming couplers. More particularly, the invention relates to such materials and processes wherein the two-equivalent pyrazolone magenta dye-forming coupler is used in combination with a ballasted phenolic solvent compound and a ballasted aniline or amine compound.
Color photographic materials employing two-equivalent 3-anilino pyrazolone magenta dye-forming couplers are known in the art as demonstrated, for example, by U.S. Pat. No. 4,853,319 and citing therein. Two-equivalent pyrazolone magenta couplers are advantageous for use in color photographic materials owing to their low cost, high efficiency, good activity, adjustable hue and suitability for use in processes without formaldehyde.
It is also known to use phenolic solvents with 3-anilino pyrazolone couplers to shift the absorption spectra bathochromically, e.g. Renner et al U.S. Pat. No. 4,952,487. The phenolic solvents may be classified as hydrogen bond donors because of their ability to supply a hydrogen bond. Such materials have been unsatisfactory from the standpoint of continued coupling which causes a non-imagewise stain.
It is also well known in the color photographic art that couplers are used in combination with solvents and other addenda which facilitate their incorporation in the photographic materials and/or improve one or more properties of the dyes formed from the couplers. For example, the Ogawa et al. U.S. Pat. No. 4,857,449 discloses combinations of couplers and one or more high boiling organic solvents for use in color photographic materials.
It has been found that the use of conventional coupler solvents such as tricresyl phosphate provide a coupler system that exhibits poor inhibition sensitivity. In other words, the copresence of development inhibitors which are either (1) unintentionally present (e.g. as the result of side reactions) or (2) intentionally added to improve image quality, have a much greater adverse effect on the coupler reactivity than is desired and can result in unacceptable degradation of other image qualities such as grain.
U.S. Pat. No. 4,483,918 Sakai et al and Furutachi et al U.S. Pat. No. 4,585,728 and Sakai et al U.S. Pat. No. 4,555,479 disclose the use of amine (including aniline) addenda with two-equivalent pyrazolone magenta couplers to reduce stain that occurs in development processing. This problem is believed to result from the fact that two-equivalent pyrazoione magenta dye-forming couplers have low pKa values. The pKa value is -log Ka, wherein Ka is the acid dissociation constant. Since these couplers tend to have low pKa values, they may be significantly ionized when films or papers coated with them are placed in solutions of low pH, i.e., a pH of 5-6, or less. Thus, when photographic materials containing these low pKa couplers are used in a process which does not employ a stop bath between the development and bleach steps, non-imagewise dye formation occurs owing to coupling with developer that is carried over into the bleach solution and oxidized therein. This phenomenon, which is referred to as continued coupling, produces undesirable increases in background density (Dmin). Continued coupling also leads to unacceptable density variability in processed films owing to variations in bleach pH as the bleach solutions become "seasoned" by continued use. Accordingly, photographic films and papers containing low pKa couplers such as the two-equivalent 3-anilino pyrazolone couplers often exhibit continued coupling because the couplers are more highly ionized at low pH and thus readily react with oxidized developer in the low pH bleach solutions. The amine materials identified by these patents are classified as hydrogen bond acceptors due to their ability to accept a hydrogen bond.
Thus, there is a need to provide color photographic materials which contain two-equivalent 3-anilino pyrazolone magenta dye-forming couplers which exhibit a reduction in the continued coupling phenomenon and which exhibit an improved inhibition sensitivity.
The achievement of satisfactory image reproduction is the result of balancing many competing factors. To maximize the saturation of individual colors it is desired to have a steeper .gamma. or contrast, but it is necessary to also have good sharpness, color purity, and low granularity. Developer inhibitor releasing couplers (DIR's)are associated with a silver halide layer to improve the sharpness and color purity, but DIR's tend to increase granularity and reduce contrast below that required for the film. Consequently, additional silver emulsion laydown would be necessary to reestablish the desired granularity and contrast. Further increases in both DIR content and emulsion laydown can be made in order to effect further improvements in sharpness and color purity, but eventually a point is reached where no more silver can be added because the image coupler is unable to react sufficiently and density no longer increases over the entire exposure range (loss of latitude). The point at which the loss of latitude occurs is a function of how much the DIR inhibits the development. The use of the phenol solvent of the present invention enables one to increase the level of DIR used to a much greater extent before loss of latitude is realized. The coupler system has less inhibition sensitivity. Sharper colors of purer color and less grain are thus obtainable than heretofore.
Accordingly, it is desired to provide improved color photographic materials and methods which employ two-equivalent 3-anilino pyrazolone magenta dye-forming couplers. It is further desired to provide color photographic materials and methods which employ two-equivalent pyrazolone magenta dye-forming couplers and which exhibit improved photographic properties such as a reduction in the continued coupling of the magenta dye-forming coupler during the bleach step of a color photographic process and also an improved inhibition sensitivity.